Orbital Signals in Carbon Isotopes: Phase Distortion as a Signature of the Carbon Cycle

Abstract

Isotopic mass balance models are employed here to study the response of carbon isotope composition (δ13C) of the ocean‐atmosphere system to amplitude‐modulated perturbations on Milankovitch time scales. We identify a systematic phase distortion, which is inherent to a leakage of power from the carrier precessional signal to the modulating eccentricity terms in the global carbon cycle. The origin is partly analogous to the simple cumulative effect in sinusoidal signals, reflecting the residence time of carbon in the ocean‐atmosphere reservoir. The details of origin and practical implications are, however, different. In amplitude‐modulated signals, the deformation is manifested as a lag of the 405 kyr eccentricity cycle behind amplitude modulation (AM) of the short (~100 kyr) eccentricity cycle. Importantly, the phase of AM remains stable during the carbon cycle transfer, thus providing a reference framework against which to evaluate distortion of the 405 kyr term. The phase relationships can help to (1) identify depositional and diagenetic signatures in δ13C and (2) interpret the pathways of astronomical signal through the climate system. The approach is illustrated by case studies of Albian and Oligocene records using a new computational tool EPNOSE (Evaluation of Phase in uNcertain and nOisy SEries). Analogous phase distortions occur in other components of the carbon cycle including atmospheric CO2 levels; hence, to fully understand the causal relationships on astronomical time scales, paleoclimate models may need to incorporate realistic, amplitude‐modulated insolation instead of monochromatic sinusoidal approximations. Finally, detection of the lagged δ13C response can help to reduce uncertainties in astrochronological age models that are tuned to the 405 kyr cycle.

Astronomical tunings of the Oligocene–Miocene transition from Pacific Ocean Site U1334 and implications for the carbon cycle

“…lithological) tuning signals can produce more accurate age models in comparison with age models based on globally integrated isotope records. The latter data are known to produce significant lags relative to eccentricity as a result of highly non-linear feedback mechanisms (Laurin et al, 2017;Pälike et al, 2006b;Zeebe et al, 2017), a result that is confirmed by this study (Table 2). The independent evidence that we provide for using a lithological (proxy) record for the astronomical age calibration of marine sediments yields further support for similar astronomical tuning methods.…”

“…7b; Laurin et al, 2017). On both the initial magnetostratigraphic age model and on the CaCO 3 tuned age model, the phase lag, as visually identified in the filtered records, between the 405 kyr eccentricity cycle and the 405 kyr cycle in δ 13 C increases during the early Miocene (Figs.…”

“…Astronomical forcing of organic carbon burial is typically expected in the precessional band because organic carbon burial, notably in the marine realm, depends on clay fluxes and thus hydrology (Berner et al, 1983). However, the residence time of carbon (∼ 100 kyr) is so long (Broecker and Peng, 1982) that this energy is transferred into eccentricity bands (Pälike et al, 2006b;Ma et al, 2011;Laurin et al, 2017). Importantly, while the total marine carbon inventory is driven by ocean chemistry, the phase lag between eccentricity forcing and δ 13 C should primarily be a function of the residence time of carbon in the global exogenic carbon pool (Zeebe et al, 2017).…”

Synchronization of the astronomical time scales in the Early Toarcian: A link between anoxia, carbon-cycle perturbation, mass extinction and volcanism

“…8A, C, D). The difference between the direct filter and the filter of the AM is explained by the residence time of carbon in the ocean, which creates a delay in the response of the  13 C to the orbital forcing (Laurin et al, 2017). In this context of hemipelagic sediments, with the limestone beds originating from exports from neritic environments, the difference may also be due to the change of the carbonate source.…”

Interhemispheric radio-astrochronological calibration of the time scales from the Andean and the Tethyan areas in the Valanginian–Hauterivian (Early Cretaceous)

“…The duration of this interval in the El Portón section is calculated at 2.15 myr, in good agreement with the Tethyan area ( Figures 10-12). The difference of 0.04 myr between the two areas may be due to the uncertainties of the correlations between the Andean and the Tethyan areas, and to the fact that the early-late Hauterivian boundary may be located within the non-marine Avilé (Laurin et al, 2017) and from the change in the source of carbonate, which change the phasing of carbonate δ 13 C relative to the insolation (Martinez, 2018). Thus, the reliable…”